Pearl oysters belonging to the genus Pinctada (Bivalvia: Pteriidae) are widely distributed between the Indo-Pacific and western Atlantic. The existence of both widely distributed and more restricted species makes this group a suitable model to study diversification patterns and prevailing modes of speciation. Phylogenies of eight out of the 11 currently recognised Pinctada species using mitochondrial (cox1) and nuclear (18S rRNA) data yielded two monophyletic groups that correspond to shell size and presence/absence of hinge teeth. Character trace of these morphological characters onto the molecular phylogeny revealed a strong correlation. Pinctada margaritifera appears polyphyletic with specimens from Mauritius grouping in a different clade from others of the French Polynesia and Japan. Hence, P. margaritifera might represent a species complex, and specimens from Mauritius could represent a different species. Regarding the putative species complex Pinctada fucata/Pinctada martensii/Pinctada radiata/Pinctada imbricata, our molecular analyses question the taxonomic validity of the morphological characters used to discriminate P. fucata and P. martensii that exhibited the lowest genetic divergence and are most likely conspecific as they clustered together. P. radiata and P. imbricata were recovered as monophyletic. The absence of overlapping distributions between sister lineages and the observed isolation by distance suggests that allopatry is the prevailing speciation mode in Pinctada. Bayesian dating analysis indicated a Miocene origin for the genus, which is consistent with the fossil record. The northward movement of the Australian plate throughout the Miocene played an important role in the diversification process within Pinctada.

This study presents a comparative analysis of population structure applied to the pearl oyster (Pinctada margaritifera) from the Central Pacific islands using three classes of molecular markers: two mitochondrial genes (mtDNA), five anonymous nuclear loci (anDNA), and eight polymorphic allozymes. Very low levels of haplotype diversity and nucleotidic divergence detected for mtDNA validate the hypothesis of a recent (re)colonization of Polynesian lagoons after their exondation during the last glaciations. Some nuclear loci, however, showed highly significant F ST values, indicating a reduced amount of larval exchange between archipelagos at present. A large interlocus variance of F ST was nevertheless observed. We discuss whether this pattern is inherent to the stochasticity of the drift process since recolonization, or if it could result from balancing selection acting on certain loci. This study illustrates once more the need to combine the analysis of several kinds of loci when unrelated phenomena are likely to leave their footprints on genetic structure.

The relationship between the shell dimensions of pearl oysters. Pinctada nmzallaiiica (Hanley 1856) and Pteria sterna (Gould lHSl), was studied to determine the possible change of form of Ihc shell during growth. The intention was to delermine the number, size and location of nuclei that could be implanted in oysters used for Mabe pearl production. Using the database of our Pearl Culture Research Programme developed in Bahia de La Paz. Mexico, we obtained measurements of 500 shells of P. mazatlaniai and 500 shells of P. sterna, representing i years of continuous growth under extensive culture conditions. The heightlength, height-thickness and the height-weight relationships of both species were analysed, as was the height-wing length relationship for /'. sterna. There was isometric growth up to tOOmm shell height, and negative-allometric growth after 120-12 5 mm for P. mazatlanica. The heightthickness relationship followed a linear model. whereas the height-weight relationship was exponential. No clear allometric pattern was found in P. sterna and all relationships litted the power equation.

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The genetic impact of the cultural practice of spat collection and translocation between genetically distinct stocks of black-lipped pearl oyster, Pinctada margaritifera cumingii, was studied by comparing samples collected in the 1980s and 2000s from seven atolls in French Polynesia. An amova revealed homogenization of the previously genetically distinct wild stocks of Tuamotu-Gambier and Society archipelagos (the indices of genetic differentiation among archipelagos and among populations within archipelagos, respectively, Phi(CT) and Phi(ST), decreased from 0.032* and 0.025*, respectively, to 0.006(NS) and 0.007(NS)). These results suggest high success of spontaneous reproduction in farms, probably due to the very high density of cultivated pearl oysters, and underline the importance of genetic monitoring of future hatchery produced stocks.